The present invention relates to optical signal detection and processing apparatus and more particularly to a three-dimensional image receiver having sensor stages with programmable gain capability.
Receivers for optical range applications require a capability for three dimensional imaging. Two out of the three dimensions are the traditional X-Y co-ordinates. The third dimension, depth, is obtained by optical ranging. For example, if a laser pulse is sent out to image a scene, the time the reflected laser pulse will arrive at the receiver depends on the range. Thus, if a large object is illuminated by a laser pulse, the reflections will not only have spatial variations due to object's structure but will also arrive at different times at the detector depending on range. The range dimension will be modulated by the object's depth or Z axis characteristics.
Imaging in three dimensions can be accomplished if two-dimensional image slices are taken at different times. Different times represent the range or distance of different features of the object from the receiver. A record of these 2-D images taken at different time intervals can be used to reconstruct a 3-D image. However, mechanization of this concept requires a special imaging receiver. Specifically, a high speed detector array is needed to take image samples of the scene at very close time intervals.
The need for programmable gain in conjunction with the visible detectors used for the ranging application is also critical. The optical signal detected varies in amplitude much like an electrical return to a radar receiver, i.e., very large levels at close ranges and low levels at long ranges. Moreover, the bandwidth required for operating these sensors (50 MHz) coupled with the low signal levels to be detected require special receivers. Optimally, a receiver which employs bandwidth compression will provide the best range performance.